Dolby Atmos for cinema playback

A more effective speaker setup

The most immediately noticeable difference in a Dolby Atmos® system is the use of overhead speakers, but that’s just part of the story.

A typical surround sound system consists of left, center, and right discrete channels with the speakers behind the screen. The surround channels are handled by wall-mounted arrays of speakers, divided acoustically into two or four zones. All speakers within a zone receive the same audio information.

In a Dolby Atmos theater, every speaker — as many as 64 total — is powered independently and gets its own separate audio feed. In effect, each speaker is its own zone. In addition to the overhead speakers, Dolby Atmos typically adds more surround speakers and screen speakers.

The improved speaker layout is a key to implementing the dramatic audio improvements of Dolby Atmos.

Sounds gain their independence

Imagine sitting in a restaurant. There’s a general buzz of conversation and music all around, yet you can pick out an individual voice behind you or a clink of silverware from the terrace above you — and you can tell exactly where each sound is coming from.

Now you’re watching that same restaurant scene in a movie. With conventional surround sound, you’ll get the ambience, but the voice and clink come from vague locations — if you can pick them out at all. That’s because channel-based sounds — particularly surround effects —have to be assigned to a general zone, not a specific location. And because there are no overhead speakers, the sounds cannot move above you.

In Dolby Atmos, each of those sounds can be created as an independent entity — an audio object. Put all the objects together, and you’ll feel like you’re actually in the restaurant, not just watching a scene.

Any sound can be a single audio object, placed and moved independently anywhere in the theater. The filmmaker decides exactly where the sound should come from and where it should move. So you hear the roar of a plane flying overhead from above you, or a door closing to the left. Sounds can originate from a single speaker or sequence of speakers, or from any number of speakers simultaneously.

Audio objects empower filmmakers to focus on the story and put the sounds where they belong, rather than compromise the artistic impact to fit a fixed channel or zone.

Making the bed

Some elements of a movie soundtrack, however, still benefit from a channel-based approach — for instance, ambient effects and music backgrounds. So a Dolby Atmos soundtrack also includes a more conventional channel-based “bed,” together with the audio objects. Dolby Atmos packages up to 128 audio tracks — a 9.1 bed and up to 118 audio objects.

Putting it together

The Dolby Atmos processor in the theater intelligently assigns each audio track. It maps the bed channels to screen channels or surround arrays, and positions objects within the room. It’s all reproduced in real time based on where the loudspeakers are. Dolby Atmos scales to the specific speaker complement of a theater, so the effects will be the same regardless of the auditorium’s size.

Sound placement is consistent throughout the audience. Thanks to audio objects originating from specific locations rather than general areas, you’ll hear the exact same effect no matter where you sit in the theater — every seat is the “sweet spot.”

Even more audio improvements

Having independently powered speakers improves the sound in other ways as well. For instance, tonal quality sometimes suffers when a sound is reproduced by an array of loudspeakers. Being able to direct that sound to single speakers makes the reproduction much more accurate and realistic.

Also, in traditional surround setups, a sound moved from the screen to the surround zones drops in volume. Dolby Atmos, using improved room equalization and better bass management along with the independently powered speakers, avoids this problem. Sounds maintain the right volume as they move, adding to the realism.

The complete Dolby Atmos system also includes authoring and distribution tools. For the full story in detail, check out our white paper.